It is known, in the slide-fastener art, to form a slide-fastener stringer or a slide-fastener stringer half by injection-molding a row of separate but identical coupling members or heads onto an edge of a support tape which may be provided with a bead or thickening such that the coupling elements or members have shanks or legs which straddle the bead or thickening and are affixed thereby to the support tape.
In the injection-molding process, a plurality of successive coupling members can be applied to the support tape simultaneously or can be molded thereon in succession. When the stringer half is completed, it is generally juxtaposed with another stringer half to form the stringer, a slider being applied to the stringer to enable the interdigitation or interfitting and separation of the rows of coupling members as the slider is shifted back and forth along the stringer.
It has been found to be necessary and desirable, in many cases, to remove one or more of the coupling members composed of thermoplastic synthetic resin from their support tapes. Such removal is desirable when a gap in a continuously produced stringer is necessary to allow the slider to be mounted upon the stringer, to permit the stringer or slide-fastener half to be secured to a fabric, e.g. of a garment, or for some other purpose, for example the application of endstop members which limit the movement of the slider.
In earlier techniques, the removal of coupling members of thermoplastic synthetic resin from their support tapes has been effected either by heating the coupling member to reduce the strength by which it adheres to the support tape, or by stamping and cutting (punching) systems which slice a portion of the support tape and/or the coupling members from the stringer half.
The heating step reduces the retention force with which the thermoplastic synthetic resin coupling member grips the support tape and hence either eliminates or reduces the clamping force by which the shanks or legs engage the tape. The heated coupling member can then be drawn off the tape.
In the stamping and cutting process, the interdigitating portions of the coupling members may be cut from the remainder thereof and, if necessary, the thermoplastic synthetic resin in the region of the crotch of the fastening shanks is removed so that the latter can be drawn off the tape.
Both these conventional techniques have been found to be disadvantageous. On the one hand, the thermoplastic synthetic resin is a poor heat conductor so that the heating of the coupling elements to a state in which they are rendered plastic, i.e. are sufficiently soft to enable their withdrawal, by convective heat transfer, is time-consuming. Heating by means of high frequency or ultrasonics is likewise costly. The stamping and cutting (punching) approach has the disadvantage that the section of the support tape in the region of the punching operation is damaged, especially when the punching tool becomes dull.
In order to explain the purposes of the coupling-member removal operation in greater detail, it can be observed that such slide fasteners are used mainly for military uniforms and sports garments. The slide fastener must be of the required length for the particular garment but is economically produced substantially continuously. In the production of such slide fasteners, the support tape is fed with a thickened edge or edge bead, through a die, and thermoplastified material is injection-molded in forms disposed at this bead so that the thermoplastic material flows around the edge of the support tape to produce a coupling member straddling same. The early attempts at such operations could only produce stringer halves of a length of 20 to 30 cm. However, with improved injection molding technology, it is now possible to operate substantially endlessly, whereby extremely long stretches of support tape can be passed through the die and successive coupling members applied thereto without interruption. Such manufacturing techniques are highly economical and relatively simple, permit coils of the stringer to be stored conveniently and to be cut into desired length only upon demand or need.
Nevertheless, the disadvantage of the continuous production of slide-fastener stringers is that the sequence of coupling members must be interrupted at given locations to enable respective sliders to be applied and to facilitate stitching of the stringer to a garment, etc. It is for this reason that systems for removing coupling elements have been investigated in the past.